A typical subsurface sewage system is comprised of a septic tank where primary treatment of wastewater takes place. The effluent wastewater is flowed to a leaching system apparatus, buried in the soil, for secondary treatment. One typical apparatus comprises serially connected leaching structure made of molded thermoplastic or concrete having perforated walls. Another apparatus comprises perforated pipes within stone filled trenches. Another comprises leaching pits, or vertical extending holes typically defined by circular cross section masonry having perforations, e.g., a precast structure or dry-laid concrete blocks. In still others, proprietary commercial devices are used, e.g., devices sold under the brand names Eljen In-Drain, Ruck A Fins, and Form Cell Living Filter. In another related type of apparatus, there is no septic tank. Raw wastewater flows into a cesspool, or covered pit, from which it leaches into the soil. In this application, any buried device that receives wastewater, to then percolate it into the surrounding soil where it is treated by microbiological action is referred to as a leaching conduit.
When wastewater flows into the soil adjacent the leaching conduits, it is naturally and microbiologically processed, to become more environmentally benign. Such adjacent soil is sometimes referred to as the influence zone. Treated waste water then typically flows from the influence zone downwardly through the soil to the underlying water table or to some other discharge point. In accord with U.S. Pat. No. 6,485,647 “Method and Apparatus for Treating Leach Fields” biochemical processing of wastewater is enhanced by flowing air or other active gas through the influence zone, preferably by flowing air under pressure into the leaching system conduit. Typically, the leaching conduit is pressurized and air flows from the conduit, through the soil, to atmosphere. In an alternate embodiment, auxiliary pipes in the soil run parallel to and spaced apart from horizontally running chambers. The auxiliary pipes are either evacuated or pressurized relative to the conduit interior, to induce flow to of from the conduit. The leaching field aeration technology can be applied to new installations, or retrofitted onto old installations. It may be used to increase capability for a system, or to rejuvenate and restore the capability of an old system.
Experience with leach field aeration installations shows that the characteristics of the soil overlying conduits may affect how air flows through the influence zone and thus diminish the potential effectiveness of the methodology. For instance, flow distribution in the soil can be affected if the soil layer is thicker or less permeable over one portion of the conduit, compared to another. Less air will flow through the influence zone associated with the more air flow-resistive overlying layer. Functional resistance to flow can be affected by such as soil constituents, water content, organic content, plant roots, and tunnels of small animals. The variations in soil resistance may be present along the length of a conduit, or from conduit row to conduit row within a system. It is often not feasible to make constant the thickness, structure, composition, and so forth, of soil overlying a leaching system, especially when the native terrain is uneven.
In some leaching system installations, the soil is topped by a bituminous pavement or analogous material which is vastly different from soil, and which pavement has either limited permeability or uneven permeability, due to changes thickness, density, cracks, and so forth.
Thus, the benefits of air flow into the leaching system can be uneven due to the nature of the overlying soil. This is especially apparent when the length of the system is long and the soil character is locally varied. Thus, there is a need to prevent or overcome such problems and obtain better distributed, or more uniform, air flow in aerated leaching systems, so the system as a whole air-enhanced biochemical processor performs near-optimally.